Public utilities are faced with the task of economically meeting a demand for electric power which undergoes hourly, daily and seasonal variations. Because of these variations in demand, it is often desirable to provide some type of bulk energy storage which stores surplus electric energy generated during periods when generating capacity exceeds demand. This is particularly applicable to nuclear powered generators because the output generally is not reduced when demand decreases. This stored energy can then be used to meet part of the demand during peak loading periods, thereby reducing the average cost of electric power generated during peak loading periods.
A variety of bulk energy storage systems are currently either under development or in use, including advanced batteries, compressed air storage, hydrogen energy storage and thermal storage. The present invention is directed to an improved form of hydrogen energy storage.
Conventional hydrogen energy storage systems employ excess electricity to generate molecular hydrogen (H.sub.2) which is then stored until needed as a fuel. The first step of generating the hydrogen may be accomplished by several methods, including the electrolysis of water. Water electrolysis is a relatively simple process which has already been employed on a large scale for several years.
However, the second step in a hydrogen energy storage system, storing the hydrogen until it is needed as a fuel, presents a range of difficulties. Several schemes for bulk hydrogen storage have been suggested, but each suffers from particular disadvantages. For example, pressure vessel storage of high pressure hydrogen is generally too expensive for use in bulk energy storage systems. Storage in natural geological cavities offers certain advantages, but suitable geological formations are not always available where needed. Cryogenic storage of liquid hydrogen is a proven method of storing large quantities of hydrogen; however, the energy cost of liquefaction and revaporization is high. Metal hydride storage, which is currently receiving much attention, has yet to be demonstrated for large scale hydrogen storage. Finally, only limited quantities of hydrogen can be mixed with natural gas for storage and transportation in conventional natural gas facilities without appreciably affecting the storage of combustion characteristics of the mixture. An ERDA sponsored committee has investigated this storage method and concluded that these appear to be no major problems in using mixtures containing up to 10% hydrogen.
The problems associated with such known methods of bulk hydrogen storage represent a significant drawback of hydrogen energy storage systems.